The Stirling cycle engine has been generally known for years and relies on the pressure variations of a closed mass of working fluid, usually a gas such as air or hydrogen, caused by the alternate heating and cooling of the working fluid which is forced by a displacer piston between communicating hot and cold spaces. A more recent development is the Beale type, free piston, Stirling engine having no direct mechanical linkage between its displacer piston and power piston and which is described in U.S. Pat. No. 3,552,120.
Such engines are mechanical oscillators which, for starting, require some initial disturbance in order to bring them from a state of static instability to oscillatory motion. This initial disturbance must be sufficient to cause some movement of the displacer piston of the Stirling engine in order to initiate further and regenerative heating or cooling amd consequent further expansion or contraction of the working gas.
Unfortunately, such initial motion is impeded by the friction between the conventional seals which separate the different spaces within the Stirling engine. Therefore, if the initial disturbance is insufficient to overcome the stick friction of the conventional seals, there may not be enough displacement of the gas to develop sufficient pressure change to continue the motion.
The surrounding environment of engines in some applications may normally provide vibrations of sufficient amplitude to initiate starting. Alternatively, such engines may be started by a sharp tap from an operator or an input from the load. However, such external sources of the initial disturbance are unreliable and there is therefore a need for means to allow the free piston engine to be reliably self-starting.